如何提取/扩展可变参数模板参数

Question

template <typename T1, typename T2>
class Base
{
  T1 t1; 
  T2 t2;
};

template <typename...TN>
class Derived
    : public Base< std::tuple<QList<TN...>>,
                   std::tuple<QVector<TN...>> > //does not work
{
};

Derived<int, double> d;

• t1 shall become std::tuple<QList<int>, QList<double>>
• t2 shall become std::tuple<QVector<int>, QVector<double>>

I don't know if this is possible in general. Currently I use preprocessor magic for that. But I hoped that variadic template can do that too. So, can I do any recursive things or any similar to extract the template?

Answer 1

As @dyp says, you expanded the pack in the wrong place. It should be like this:

: public Base< std::tuple<QList<TN>...>,
               std::tuple<QVector<TN>...> >